Consistent, Around the 100-105km/h mark it comes on, and stays on until traffic slows me down etc, i can shift down to 5th, or stay in 6th it's still there, just a little harder to hear in 5th for obvious reasons

Edit - Also if it helps, I have noticed it gets a hell of a lot louder if I turn the steering wheel a tiny little bit (Like going around slight bends)